Low voltage ion source



vMarch 12, 1957 E. O. LAWRENCE i; 8 6 l: :i 24

r= I7 5** i/ rs@ 7 23 L. 22 2l/ rh MAGNET 3/f PowER SUPPLY 33w `FILMENT ARG VOHLIlAHGE PowER PowER PowER 32j SUPPLY SUPPLY k- SUPPLY INVENTOR. ERNEST 0. LA wRENcE BY /KM// wf/m T TORNEX nited States Patent LOW VGLTAGE 19N SOURCE Ernest 0. Lawrence, Berkeley, Calif., assigner te the United States of America as represented by the United States Atomic Energy Commission Application June 24, 1952, Serial No. 295,153

9 Claims. (Ci. ZEG-41.9)

The present invention relates to an improvement in ion generators and particularly to the production of a very high current ion beam. Conventional ion sources or generators are limited to the production of a relatively weak ion beam and despite forcing, even without regard to ehciency, it is very dir'licult to produce a strong ion beam. Generally the ion beam is limited by the ion extraction process, for even though a very high current arc discharge be attained an upper limit is imposed upon the number of ions that can be removed from the arc.

The present invention is adapted to remove or obviate the limiting factors in ion ejection from an arc or the like. Probably the most important of those factors is space charge which effectively limits the ion current that may be drawn through a given aperture, and the present invention practically eliminates space charge effects so that the upper limit upon the ejected ion beam is thus dependent upon the arc intensity which in turn is limited only by the power available for the arc. Not only is the present invention capable of ejecting an intense ion beam but it also is much more eicient than other relatively high intensity ion sources and does not rely entirely upon brute torce to eject ions.

lt is an object of the present invention to provide an improved ion source producing a high current ion beam.

lt is another object of the present invention to provide an improved ion source producing a plurality of small ion beams focused into a single high current beam.

it is a further object of the present invention to provide an improved ion source producing a high current ion beam with small angular divergence.

Numerous other advantages and objects of the invention will become apparent from the `.following description or' the invention taken together with the attached drawing wherein the soie figure illustrates one preferred embodiment of the invention with appropriate electrical apparatus connected thereto.

Referring to the drawing, there is shown in part a housing 11 which may be adapted for connection to or in an evacuated vessel in which an ion beam is desired, as for example a particie accelerator. The end wall 12 of housing 11 may be removably mounted as by bolts for easy access to the source proper. Within housing 11 there is disposed a cylindrical anode 13 which may be mounted upon end wall 12 and which has a relatively thick exit grid 14 mounted in closing relation to the innermost end of anode 13. Disposed within anode 13 is a cathode 16 which may comprise a coiled filament of rather large wire to carry heavy heating currents. Cathode 16 is disposed to lie crosswise in anode cylinder 13 at a distance from exit grid 14 and may be supported in this position by a pair of rigid conductors 17 which extend through end wall 12 in insulated relation thereto and are xed to opposite ends of the ilament coil 16. A gas tube 18 extends through end wall 12 of housing 11 into anode cylinder 13 to provide a 2,785,311 Patented Mar. 12, 1957 gas to be ionized within the source and for this purpose may be connected to a gas supply (not shown) external to the source.

Disposed about cylinder 13 are magnet windings 19 which are mounted either upon cylinder 13 or suspended from housing 11 as by means of brackets 21. A pair of electrical conductors 22 are attached to opposite ends of magnet winding 19 and extend through a wall of housing 11- in insulated and vacuum tight relation thereto for connection to appropriate magnet energizing means external to housing 11. There are also provided within housing 11 a plurality of accelerating grids shown as two grids 23 and 24 which have substantially the same curvature as exit grid 14. Accelerating grids 23 and 24 are disposed parallel to exit grid 14 exterior to anode cylinder 13 and are situated quite close to exit grid 14 and to each other with irst accelerating grid 23 being intermediate exit grid 14 and accelerating grid 24. The above grid relationship, is maintained by suitable mounting of accelerating grids, such as illustrated. This mounting may be accomplished by the provision of a liange or extension 25 about the end of anode cylinder 13 to which are attached insulators 26. Accelerating grids 23 and 24 are provided with extensions which may be bolted to insulators 26, as shown, and which therefore carry grids 23 and 24. Electrical conductors 27 and 28 are connected to the extensions of grids 23 and 24, respectively, and together with another conductor 29 connected to anode cylinder 13 are brought out of housing 11 in insulated and vacuum tight relation thereto for connection to appropriate sources of voltage.

in conjunction with the above-described elements of the ion source there is provided `an electrical energization system located without housing 11 and connected to the source elements. The illustrated electrical system includes a magnet power supply 31 having magnet leads 22 connected thereto and energizing magnet windings 19 therethrough to produce a magnetic field H having lines of force through and parallel to the axis of anode cylinder 13. A filament power supply 32 provides heating current for cathode 16 by means of electrical connections between filament conductors 17 and larnent power supply 32. A high Voltage power supply 33 is either provided with voltage taps or is connected across a resistor 34 having a number of taps thereon. Anode lead 29 is connected to one end of resistor 34, which may be grounded, and grid leads 27 and 2S are connected to appropriate points on resistor 34 to apply the desired portion of the voltage thereacross between anode 13, grid 23, and grid 24. An arc power supply 36 is connected between anode lead 29 and one of the lilament conductors 17 to provide power to produce an arc discharge within anode 13. The above electrical components may provide either a continuous or pulsed voltage depending upon the desired mode of operation of the source, and in this respect, it has been found advantageous to use an alternating current filament supply and tor pulsed operation to pulse the magnet and arc power supplies.

Considering now the operation of the invention, energization of nlament power supply 32 will cause cathode 16 to become electron emissive and with a large heating current and relatively rugged cathode structure a large number of electrons are made available for acceleration from cathode 16. Energization of magnet power supply 31 establishes a magnetic eld H having lines of force through anode cylinder 13 substantially parallel to the axis thereof, whereby electrons emitted from cathode 16 are constrained to travel along the magnetic lines of force. Energlzation of arc power supply 36 establishes a strong electrostatic eld between anode 13 and cathode 16 attracting electrons away from cathode 16. These .electrons are ice 6. An improved high current ion source comprising a cathode having a large electron emissive surface, an electrode formed of a material resistant to ion and electron bombardment disposed in spaced relation with said cathode and facing the electron emissive surface thereof, said electrode having a plurality of individual spaced apertures therethrough, power supply means connected between said cathode and electrode for producing an arc discharge therebetween, and ion accelerating means maintained at a negative potential with respect to said elec trode and disposed on the opposite side thereof from said cathode whereby ions from said arc are electrostatically attracted through the apertures in said electrode to form a plurality of individual ion beams adapted to be joined to form a high current ion beam.

7. An improved high current ion source comprising means estabiishing an arc discharge, ion accelerating means disposed across one end of said arc for attracting ions therefrom, and an electrode disposed intermediate said arc and said ion accelerating means and having a plurality of separated apertures therethrough in line with said arc through which ions are attracted by said ion accelerating means to form a plurality of ion beams.

8. An improved ion source as claimed in claim 7 further characterized by said apertured electrode being c011- vex with respect to the end of said arc, said ion accelerating means comprising a plurality of nested grid electrodes disposed substantially parallel to said apertured electrode and with small spacing between electrodes, and

a power supply connected to said grid electrodes and maintaining each of said electrodes at a negative potential with respect to the next adjacent electrode toward said arc discharge whereby said individual ion beams are accelerated in increments and are focused together into one high current ion beam at a distance from said ion acceleration means.

9. An improved high current ion source comprising a cathode having a large electron emissive surface, an anode including an exit grid structure having a plurality of separated apertures therethrough and facing the electron emissive surface of said cathode, means for establishing a magnetic field having lines of force extending between said cathode and exit grid, an arc power supply connected between said anode and cathode for producing an electron discharge from said cathode to said exit grid directed by said magnetic field, means supplying said electron discharge with a gas to be ionized whereby said electron discharge becomes an arc discharge, and ion attraction means disposed adjacent said anode exit grid on the opposite side thereof from said cathode whereby ions are attracted from said arc through the apertures in said anode exit grid to form a plurality of individual ion beams emerging from said ion source.

References Cited in the tile of this patent UNITED STATES PATENTS 2,570,124 Hemqvisr v.- oct. 2, 1951, 

